Senescent glia link neuronal mitochondrial dysfunction and lipid droplet accumulation with age [19082-12_MASTER]

Senescence is a cellular state linked to aging and age-onset disease across many mammalian species. Acutely, senescent cells promote wound healing and prevent tumor formation; but they are also pro-inflammatory, thus chronically exacerbate tissue decline. While senescent cells are active targets for anti-aging therapy, why these cells form in vivo, how they affect tissue aging, and the impact of their elimination remain unclear. Here we identify naturally-occurring senescent glia in aged Drosophila brains and decipher their origin and influence. Using AP1 activity to screen for senescence, we determine that senescent glia can appear in response to neuronal mitochondrial dysfunction. In turn, senescent glia promote lipid accumulation in non-senescent glia; similar effects are seen in senescent human fibroblasts in culture. Targeting AP1 activity in senescent glia mitigates senescence biomarkers, extends fly life and health span, and prevents lipid accumulation. However, these benefits come at the cost of increased oxidative damage in the brain, and neuronal mitochondrial function remains poor. Altogether, our results map the trajectory of naturally-occurring senescent glia in vivo and indicate that these cells link key aging phenomena: mitochondrial dysfunction and lipid accumulation. To determine if fly AP1+ glia have features of senescent mammalian cells, we FACS-sorted and bulk-RNA-sequenced three distinct cell populations from aged fly brains (40 d): neurons, AP1+ glia, and AP1neg glia. For this, glia were labelled with GFP expressed under a constitutive pan-glial driver (repo-GAL4) while cells with AP1 activity were identified using a genomic dsRed fluorescent reporter under the control of an AP1 binding motif. Whole brains were dissected from aged flies (40 d) and dissociated into a cell suspension. Neurons (dsRednegGFPneg), AP1neg glia (dsRednegGFP+) and AP1+ glia (dsRed+GFP+) were then FACS-isolated and bulk RNA-sequenced for downstream gene expression analysis (n=500 cells per biological replicate, 4 replicates). Using the same approach described above, we also isolated and sequenced neurons from 5 d fly brains for comparison to aged neurons.